The objectives of these studies are 1) to develop animal models for investigating the feasibility of transferring reject heat from existing and projected implantable devices across the walls of intact blood vessels to the circulating blood; 2) to develop similar models for investigations of the feasibility of similar heat transfer across fixed or flexing vascular prostheses containing viable or nonviable neointima; and 3) to investigate the feasibility of transferring reject heat from existing and evolving left ventricular assist devices containing metallic heat exchangers in contact with the blood in systems compatible with (or containing) implanted nuclear power sources. The specific objectives of these studies over the past year have been: a) to study animal models with heated, non-coated, straight-tube heat exchangers; b) to study heat transfer characteristics of blood pump heat exchangers in vivo; c) to perform in vitro blood pump heat exchanger experiments with non-treated surfaces; d) to characterize biologic/biomaterials interfaces.